Flare stacks are widely used for combustion of combustible fluids such as waste gasses occurring at gas- or oil drilling sites, or liquids or process gasses at various chemical and petrochemical applications.
Most widely used flare stacks are of the open combustion type. Flare stacks combust fluids by means of a flame, where a burner assembly is mounted on top of a high stack. The combustion is done using open flames, possibly assisted by steam or compressed air for creating turbulent gas streams. An example is provided in U.S. Pat. No. 5,649,820. Such combustion may cause not only incomplete combustion, but also may cause thermal nuisance, noise and/or light pollution.
As an alternative, enclosed combustion may be used for flaring such waste or process fluids. As an example, NL1011009 describes such enclosed burner assembly for combustion of combustible gasses. Also JP53-98530 describes a flare stack using enclosed combustion of fluids. A more recent example flare stack is e.g. described in WO 2006/010693.
The presently known flare stacks are limited in capacity due to the specific build up of such a complete premix surface combustion chamber. Variations in flow and gas composition affect the air/gas ratio and can result in an instable combustion process generating smoke, odors and/or light.
In normal conditions, most flare or advance waste gas combustion systems have a turndown ratio (i.e. ratio of maximum to minimum firing rate on a modulating burner) of 5:1 to maximally 10:1. Higher turndown ratio's would allow the flare stack to handle a broad range of capacities.
The presently known flare stacks all require an operator to control the air excess for the premix, control safe operation and shutdown.